John Dickerson is a co-anchor of CBS This Morning, co-host of the Slate Political Gabfest, host of the Whistlestop podcast, and author of Whistlestop and On Her Trail.

If Mitt Romney is the nominee, conservatives will have to reverse themselves on the idea of constancy itself. His flips are numerous and on videotape. Gingrich would need persuade two of the most powerful forces in modern Republican politics to reverse themselves. Social conservatives and Tea Party activists would appear to have insurmountable objections to Gingrich. Social conservative leaders have long argued that presidents must have a sterling private history. Gingrich has the most checkered personal past in the Republican field, with two divorces and an admitted adulterous affair. Tea Party activists, meanwhile, largely blame establishment politicians in both parties for government bloat and a system that rewards the well-connected and influential. Gingrich was in Congress for 20 years and afterward joined the non-elected establishment, making millions working for Freddie Mac and other private companies seeking influence and advice in Washington.

Gingrich appears to be well on his way to winning over social conservatives and Tea Party supporters in Iowa. Gingrich is the front-runner and leads Romney by between 8 and 9 points in the most recent Des Moines Registerpoll and the NBC/Marist poll.

Social conservatives have played a key role in the state, voting Pat Robertson to second in the 1988 caucuses and giving Mike Huckabee the win in 2008. The polls show evangelical voters backing Gingrich, who regularly and freely admits his past sins. (Thirty-one percent of evangelical voters support him in the Marist poll; Romney, the next closest competitor gets 14 percent.) Mitt Romney was the one who was supposed to be helped by the fact that social conservatives were going to be less focused on family values issues in this election. Right now Gingrich appears to be benefitting.

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Gingrich also doesn’t seem to be hurt by his Washington credentials. Before Herman Cain ended his candidacy, his campaign called voters who had previously told volunteers they planned to vote for Cain. twenty-five percent of the committed dropped off, according to former Cain Iowa Chairman Steve Grubbs. 83 percent of those departing Cain voters—who had backed the candidate who based his campaign on a lack of Washington experience—said they were supporting Gingrich.

He is leading in the Iowa polls and in other states because voters want to be inspired by a conservative message. Mitt Romney doesn’t do that. When voters were asked by the Des Moines Register which candidate is most like Ronald Reagan, Gingrich was at 25 percent, 14 points ahead of Romney. He also bested Romney by double-digit margins on questions of experience, knowledge, and which candidate is likely to bring about change. Romney, who has never been a Washington politician, has run a risk-free, establishment campaign. Gingrich, the consummate insider, comes across as the bomb-throwing radical.

Gingrich represents a much more serious challenge to Romney than Michele Bachmann, Herman Cain, or Rick Perry ever did. When other candidates challenged Romney, his advisers could say that he still held the two trump cards. He was the candidate voters thought could handle economic issues—their No. 1 concern—and he was the candidate they considered most likely to beat Barack Obama. Not so much anymore. When asked which candidate can better turn around the economy, Gingrich wins 22 percent of the support and Romney 20 percent. The electability question is less clear, but still not a clean win for Romney. In the Des Moines Register poll, when people were asked which candidate was more electable, Romney got 38 percent to Gingrich’s weak 22 percent. But in the Marist poll, 38 percent of those whose key concern was beating President Obama picked Gingrich, compared with 25 percent who supported Romney. (UPDATE: The latest Washington Postpoll in Iowa shows Gingrich beating Romney on the question of which candidate can beat president Obama and which one they trust to handle the problems facing the economy.)

Gingrich is the candidate voters think could better handle a crisis in the Oval Office, though Romney is the one they think is more presidential. Voters also find Romney more likable. For the moment, though, these are not the qualities they’re motivated by.

Gingrich's strong showing in Iowa doesn't necessarily mean voters have given up on their principles. It may mean that they don’t know about his past. In the Marist Poll, 59 percent said it would be unacceptable for a nominee to have “earned millions of dollars advising Freddie Mac.” It's now up to Mitt Romney—or a Super Pac working on his behalf—to make sure voters get a thorough education. He’d better hurry up. The caucuses are 29 days away, but longtime Iowa hands say the window of change is shorter than that. After Dec. 20, Iowa voters start paying attention to their families and the end-of-year football games—particularly the Hawkeyes vs. Sooners game. That gives Romney about two and a half weeks.